A mechanical-type electric switch is a manually operated electromechanical device. Its function is based on attaching or detaching two metal conductors to produce a short or open circuit, respectively. This mechanical-type switch is not suitable for installing in a space where has the concern of gas explosion, because an instantaneous surge current, produced by suddenly engaging or releasing the metallic contact of the switch, may generate electric sparks to ignite fire.
A controllable semiconductor switching element, such as a triac, has nearly zero voltage between two output-electrodes in conduction mode and nearly zero current through two output-electrodes in cut-off mode. Solid state electronic switch utilizing the above unique features of triac for circuit on/off switch control can avoid generating electric arc, since the main current pathway of the solid-state switch is not formed by engaging the two metal conductors. It becomes a much better choice than mechanical-type electric switch from the stand point of safety consideration.
Solid-state electronic switches are constructed with various methods to trigger controllable switching element, like triac or thyristor, into conduction or cutoff for desired electric power transmission. For example, U.S. Pat. No. 4,322,637 disclosed a technique using optical coupling element to control bi-directional thyristor or triac in conduction or off state; or another U.S. Pat. No. 6,285,140B1 disclosed a technique using microcontroller incorporated with zero-crossing-point detector to generate AC-synchronized time-delay pulse to control triac in on or cut-off state so as to transmit variable electric power to a light-emitting diode load.
Mostly a mechanical toggle or spring button of similar setup is usually applied on the electronic switch to facilitate manual on/off switch operation. The operation of electronic switch with mechanical toggle means an inevitable contact by hand which is not appropriate in working places such as kitchens or hospitals. To relieve concerns of contagion or contamination resulted through hand contacts, touchless switches are developed. For example, U.S. Pat. No. 5,637,863 disclosed a technique utilized infrared sensor to activate electronic switch to operate on/off switch control, and even dimming control presumably by modifying its circuit design.
In retrospect, the above mentioned prior arts have however still some drawbacks. For instance, U.S. Pat. No. 5,637,863 used a complicated infrared sensor construction and circuit design; or U.S. Pat. No. 6,285,140B1 did not resort to an efficient control of electric power transmission from power source to various electric impedances which is required in lighting apparatus.